Electric current converting means



June 8, 1965 E. o. SCHWEITZER, JR 3,188,544

ELECTRIC CURRENT commune MEANS Original Filed June 2'7, 1956 90PHA5E UGENERATOR 5H'FTER msausrvay DOUBLER mmvrox idfizwz/diclzzz/agei; J/

United States Patent '5 Claims. (Cl. 318-257) This invention relates,generally, to electric current converting means and it has particularrelation to converting alternating current to direct current. Thisapplication is a division of application Serial No. 594,322, filed June27, 1956, now abandoned, as a continuationin part of application SerialNo. 576,564, filed April 6, 1956, now Patent No. 3,004,381, issuedOctober 17, 1961.

Among the objects of this invention are: To convert a pair ofalternating currents having a fixed relation to each other to directcurrent; to vary the magnitude and direction of flow of the directcurrent by shifting the relative phase positions of the alternatingcurrents; and to employ the direct current output for operating a motoror like device requiring variations in magnitude of current flow orreversal of current flow for operation or for other purposes.

The single figure of the drawing illustrates, diagrammatically, how thebridge circuit of the present invention, having non-linear currentconducting devices in each of the branches, can be employed forcontrolling the operation of a device such as an electric motor.

Referring now particularly to the drawing, it will be observed that thereference character 25 refers to a bridge circuit which employs fourdevices 26, one in each arm, which have nonalinear current carryingcharacteristics. In this instance it is desired to obtain a substantialamount of power from the bridge circuit. 25 and to employ relatively lowfrequency for producing the required amount of direct current. For thispurpose it is possible to use tungsten filament lamps or thyritevaristors for the devices 26. The direct current terminals 27 of thebridge are connected through a capacitor 28 to a source 29 of doublefrequency, for example, a frequency of 60 cycles per second. The source29 is a frequency doubler which is energized from a source 30 ofalternating current, such as a 30 cycle generator. Provision is made bymeans of a 90 phase shifter 31 for shifting the phase of the 30 cyclecurrent with respect to the second harmonic or output of the frequencydoubler 29. A hand wheel 32 is employed for manual control. It will beunder-stood that the phase shifter 31 may be of the type described inthe above applications for shifting the phase through 360 but arrangedmerely to employ only one-fourthof its range since a complete reversalof the polarity applied to the terminals 27 can be obtained through a 90phase shift as will be understood readily. The output from the phaseshifter 31 is applied to the terminals 33 of the bridge 25. It will beunderstood that the phase of the second harmonic from the frequencydoubler 29 can be shifted with respect to the phase of the output of the30 cycle generator 30, if desired.

A load device, such as a direct current motor shown generally at 34, isconnected between the terminals 27.

It may include an armature .35 and a series field winding 36 connectedin series circuit relation therewith. In addition, a separately excitedfield winding 36' is employed and is energized from a suitable directcurrent source, such as a battery 36".

By shifting the position of the phase shifter 31 by the hand wheel 32 orother suitable means, it is possible to change the magnitude andpolarity of the direct current flowing between the terminals 27 and thusto change the speed and direction of rotation of the armature 35.

It is possible to omit two of the nonlinear devices 26 from the bridge25 and employ in lieu thereof resistors or a potentiometer. However, theoutput of the bridge is decreased by over fifty percent if only two ofthe nonlinear current conducting devices 26 are used.

What is claimed as new is:

1. A motor control system comprising, in combination, a four arm bridgecircuit having in at least each of two adjacent arms a non-linearresistance device, means for energizing a pair of opposite terminals ofsaid bridge circuit from a source of alternating current, means forenergizing the remaining pair of opposite terminals of said bridgecircuit at least one of which is between said non-linear resistancedevices from a source of alternating current the frequency of which istwice that of the first mentioned alternating current, a direct currentmotor connected between said remaining pair of terminals, and means forshifting the phase of one of said alternating currents with respect tothat of the other to vary the operation of said motor.

2. A motor control system comprising, in combination, a four arm bridgecircuit having in at least each of two adjacent arms a non-linearresistance device, means for energizing a pair of opposite terminals ofsaid bridge circuit from a source of alternating current, means forenergizing the remaining pair of opposite terminals of said bridgecircuit at least one of which is between said non-linear resistancedevices from a source of alternating current the frequency of which istwice that of the first mentioned alternating current, a direct currentmotor having armature and field windings one of which is separatelyexcited and the other is connected between said remaining pair ofterminals, and means for shifting the phase of one of said alternatingcurrents with respect to that of the other to vary the speed anddirection of rotation of said motor.

'3. The invention, as set forth in claim 1, wherein each of the fourarms of the bridge circuit includes a nonlinear resistance device.

4. The invention, as set forth in claim 1, wherein the non-linearresistance device is a tungsten filament lamp.

5. The invention, as set forth in claim 1, wherein the non-linearresistance device is a thyrite varistor.

References Cited by the Examiner UNITED STATES PATENTS 2,104,801 1/38Hansell 318-318 X 2,648,811 8/53 Sohon 321-59 2,714,635 8/55 Schmitt307-2 2,749,499 6/56 Hosticka et al. 321--60 2,876,408 3/59 Alexanderson318345 ORIS L. RADER, Primary Examiner.

2. A MOTOR CONTROL SYSTEM COMPRISING, IN COMBINATION, A FOUR ARM BRIDGECIRCUIT HAVING IN AT LEAST EACH OF TWO ADJACENT ARMS A NON-LINEARRESISTANCE DEVICE, MEANS FOR ENERGIZING A PAIR OF OPPOSITE TERMINALS OFSAID BRIDGE CIRCUIT FROM A SOURCE OF ALTERNATING CURRENT, MEANS FORENERGIZING THE REMAINING PAIR OF OPPOSITE TERMINALS OF SAID BRIDGECIRCUIT AT LEAST ONE OF WHICH IS BETWEEN SAID NON-LINEAR RESISTANCEDEVICES FROM A SOURCE OF ALTERNATING CURRENT THE FREQUENCY OF WHICH ISTWICE THAT OF THE FIRST MENTIONED ALTERNATING CURRENT, A DIRECT CURRENTMOTOR HAVING ARMATURE AND FIELD WINDINGS ONE OF WHICH IS SEPARATELYEXCITED AND THE COLOR IS CONNECTED BETWEEN SAID REMAINING PAIR OFTERMINALS, AND MEANS FOR SHIFTING THE